Hand-held striking tools, such as claw hammers, mallets, sledge hammers, ball peen hammers, masonry hammers, pickaxes, and the like, have been used by people in a variety of disciplines for centuries as leveraged devices to provide a striking force to accomplish a seemingly endless variety of tasks. For example, a claw hammer, commonly weighing from 7 to 32 ounces is used by people doing carpentry work to deliver sufficient striking force to drive a nail into wood. A claw hammer is also used for removing a nail or ripping apart lumber using it's claw. A sledge hammer, commonly weighing from 2 to 20 pounds, is used to deliver sufficient striking force for heavy work such as driving a stake, awl drill, chisel, or driving a wedge into masonry, stone, wood, or other hard materials.
Another common hand-held striking tool is a ball peen hammer, which has a substantially flat surface on one end and a rounded surface on the other end of its head, and is used to deliver sufficient striking force for shaping and fitting metal, and for driving machine chisels, rivet sets, machine wedges, and other similar tools. A pickaxe is another example of a hand-held striking tool which is commonly used for loosening hard dirt and stones, and also used as a lever for prying heavy objects from the ground. Another common hand-held striking tool is a mallet, which is usually made of wood, plastic, rubber, or soft iron. A mallet provides a striking force to drive chisels or shape metal and other materials without significantly marring the material it strikes.
Hand-held striking tools, such as those described above, are commonly used as third-class levers used to provide a striking force to accomplish tasks such as driving a nail into a piece of wood, bending or forming metal, breaking a rock, and other similar tasks. Third class levers are levers where a fulcrum, also referred to as a pivot point, is at one end of a bar or rod. A load to be overcome is an object creating resistance at the opposite end of a bar or rod. An effort, or force, to be applied to a third-class lever is somewhere in between a fulcrum and load. In the case of a hand-held striking tool such as a claw hammer, the fulcrum is a wrist, the force is provided by deceleration of the movement of a hammer handle (bar or rod) at the wrist, and the load is a resistance presented by a piece of wood into which the nail is being driven.
In another example, a hand-held striking tool such as a pickaxe, the fulcrum is also a wrist, the force is provided deceleration of the movement of a pickaxe handle (rod) at the wrist, and the load is a resistance presented by dirt or stones into which the sharp point of the pickaxe is driven.
The head of a hand-held striking device is commonly a significant distance from the fulcrum and moves faster than the movement being applied at a user's hand, which is near the fulcrum. The increased speed of the head multiplies the applied force with which a striking device head strikes a nail or digs into the dirt. The longer a claw hammer's handle, for example, the faster the head and the greater the force that strikes a nail and overcomes the resistance of the wood. This principle applies to all other hand-held striking devices, and is intensified in long-handled striking devices such as a pickaxe or an axe.
Hand-held striking tools are also commonly used as first-class levers to provide a lifting or prying force to accomplish a variety of tasks. For example, some hand-held striking devices are used to pull nails out of a pieces of wood, tear apart pieces of wood or other building material, pry loose a large rock, lift a log, and the like. First class levers are levers wherein the load to be overcome is at or near one end of a rod or bar, the effort, or force is applied at or near the other end of the same rod or bar, and the fulcrum, or pivot, is somewhere along the rod or bar in between the applied force and load.
An example of a hand-held striking tool being used as a first class lever is a claw hammer being used to pull out nails, wherein the load to be overcome is the wood causing friction against an embedded nail. Another example of a hand-held striking tool being used as a first class lever is a pickaxe being used to pry out a rock or tree root embedded in dirt or rock, where the load to be overcome is the dirt or rock causing friction against an embedded rock or tree root. Whenever a hand-held striking tool is used as a first class lever, the force is applied at one end of a long handle. The fulcrum is typically near the other end of the handle which holds the head.
The load for a hand-held striking tool being used as a first class lever, such as in a claw hammer or a pickaxe, is typically very close to the fulcrum. Whereas the force for a hand-held striking tool being used as a third class lever is typically relatively far away from the fulcrum. During prying or pulling tasks, the load applied is therefore moved less distance than the hand, which is at the opposite end of the lever, and applying the force. This multiplies the force in which the claw hammer head pulls against a nail, or a pickaxe pulls against a rock.
The weakest part of a hand-held striking device is the interface between the handle and the head. The conventional method of interfacing a striking device head and handle, which are typically made of distinct materials, such as metal and wood, allows striking and pulling stresses to promote head-to-handle loosening, damage, and separation. For example, the impact force at the head of a claw hammer, being used as a third class lever against a nail, is often as high as 300 pounds. Because of the greater length of its handle and greater weight of its head, the striking force of the head of a pickaxe against the earth is many times greater.
The bending moment applied at the head-to-handle interface of a claw hammer being used as a first class lever to pull out a nail is often as high as 1,000 foot-pounds. The bending moment levied against the head-to-handle interface of a pickaxe pulling heavy rocks away from the earth is typically many times more.
The effect of these forces is exacerbated when a user occasionally misses his target and strikes the handle of such a tool against a hard object, such as the edge of a piece of wood, or a rock, at the head-to-handle interface just below the head. This causes further damage and weakens a head-to-handle interface.
Because of the inherent weakness in conventional head-to-handle interfaces, it is at this point that most failures in hand-held striking devices occur. Methods have been devised to make head-to-handle interface configurations capable of withstanding impacts and pulling stresses described above without damage. These methods include using a handle made with a material, such as high-impact plastic or heavy-gage rolled steel, that has particularly high strength and resiliency to withstand extremely high impacts and pulling stress. These types of handles are typically encapsulated in a resilient material, such as natural or synthetic rubber, leather, or plastic, to provide some protection from the shock from impact and to give a user a good grip on the handle. Many users of hand-held striking devices, however, still prefer the look and feel of wooden handles.
As stated above, a problem with many conventional methods for increasing handle strength on hand-held striking devices is the inherent weakness in the design of interfaces. Current interfaces for hand-held striking tools typically comprise a handle whose end is shaped to make a tight fit through a shaped opening in the head. Such a shaped opening is often tapered so the fit can be tightened by driving the head in the direction against the taper. This interface is typically made secure by a variety of methods. In one conventional method, for example, wooden handles are often secured by metal or wooden wedges or cylinders forced into the top of the handle after the handle is inserted into the head. This expands the wood so it makes a tight fit against the inner surfaces of the opening. A tight fit, however, does little to increase the strength of the conventional head-handle interface.
In another method, metal handles may be made tight to a head with an opening by heating the head and/or cooling the handle significantly to create a relatively loose fit. This allows easy insertion of the handle into the hole in the head. After insertion of a handle into the hold in a head, the metal head and handle return to ambient temperature, and the opening in the head contracts and/or the metal handle expands to produce a tight fit.
Another common method for securing conventional head-to-handle interfaces is by placing a bonding material, such as an epoxy adhesive, between the inner surface of the opening in the head and outer surface of the interface end of the handle.
The types of head-to-handle interfaces and methods of securing described above are commonly used on all types of hand-held striking tools, such as axes, sledge hammers, pickaxes, and the like. A problem with these conventional solutions is that the striking and pulling forces are concentrated over a short distance at the interface. The intensified stress at this small area is the cause of most hand-held striking tool failure. Head-to-handle interfaces made according to conventional art, regardless of the material of the handle or method of securing it to the head opening, often fail because of this concentrated stress.
As describe earlier, hand-held striking devices typically come in a variety of weights, depending upon the task at hand or the physical condition of the user. For example, claw-hammers used for general carpenter work, commonly referred to as a curved-claw nail hammer, are typically manufactured and sold in weights from 7 to 20 ounces. Claw hammers designed and used for rough work such as framing, opening crates and prying apart boards, commonly referred to as ripping hammers, are typically manufactured and sold in weights from 20 to 32 ounces. The primary difference between a curved nail hammer and a ripping hammer is that the ripping hammer has a substantially straighter and longer claw than a curved nail claw.
Another example of weight variations in hand-held striking tools are sledge hammers. These hand-held striking devices are used to apply heavy duty striking forces against objects. They are manufactured and sold in weights from 2 to 20 pounds. Many other striking tools, such as pickaxes, axes, mallets, and the like also are typically manufactured and sold in a range of weights to suit the needs of a user.
A user, particularly a professional, commonly may need a hand-held striking tool in two or more weights to accommodate a particular task at hand or his current physical condition. Assume, for example, a carpenter lying on his back inside an attic of a small alcove at a home construction site installing braces above him. He or she might prefer a light nail-pulling hammer, such as 16 ounces, to accommodate the fact that he or she must swing the hammer up against gravity with a small space for arm movement. The same carpenter, who later moves to a different home construction site to remove foundation forms and install floor joists may choose a heavier ripping hammer, such as 30 ounces. This will enable him or her to take advantage of the downward force of gravity and greater area to swing the hammer. A disadvantage in current art is, in situations like these, the carpenter must purchase and care for two or more separate hammers, which adds to his cost and maintenance.
As described above, the common two types of claw hammers are the curved-claw nail hammer, used for light carpentry work, and the ripping hammer, which is typically used for heavy rough work with wood. A curved-claw nail hammer is well suited for pulling nails because the curve of its claw provides increased leverage because the nail (load) is placed close to the end of the handle near the lever's fulcrum. A curved-claw nail hammer is not well suited for ripping tasks because the curve of its claw makes it difficult to fit between planks and make a direct cutting blow to tear into materials, such as plaster wall.
A ripping hammer, on the other hand, is well-suited for tearing apart planks and breaking into materials, such as a plaster wall, because its relatively straight claw fits more readily between planks and angles, and its cutting edge (wedge) points directly away from the hammer's head. A ripping hammer is typically not well-suited for pulling nails because the width of its claw to ensure adequate ripping strength preclude placing a nail pulling slot close to the fulcrum for increased leverage. A user, particularly a professional, often purchases one or more curved-claw nail hammer and one or more ripping hammer to accommodate his or her need to perform specialized nailing or ripping tasks. This adds to a user's costs and maintenance for their care.
What is clearly needed is a head-to-handle interface for hand-held striking devices that can minimize bending stresses at head-to-handle interface when using a wooden handle, or a handle made from any suitable material.
What is also clearly needed is a method to change the weight of a hand-held striking device to accommodate a user's changing weight needs without purchasing two or more of the same type of striking device.
What is also clearly needed is a claw hammer that is equally suitable for pulling nails as it is for ripping boards and other materials to accommodate a user's changing needs without requiring the user to purchase two or more different claw hammers.